Project Summary/Abstract Acetaminophen (APAP) is a safe analgesic and antipyretic drug commonly used as a pain reliever and fever reducer. However, intentional or accidental APAP overdose leads to hepatocyte cell death and is the major cause of acute liver failure (ALF) in the U.S. The measurement of blood biomarkers of mitochondrial damage draws a parallel in the clinic with unfavorable outcome in overdose patients. Moreover, recent findings on the protective effect of agents that promote mitochondrial glutathione recovery and mitochondrial superoxide dismutase action reveal that mitochondrial oxidant stress (reactive oxygen species, ROS) and peroxynitrite (RNS) formation and ATP depletion are fundamental steps in the pathophysiology of APAP induced liver injury in mice and humans. The only approved clinical therapy to remedy this APAP-induced mitochondrial toxicity is the administration of N-acetyl cysteine (NAC). NAC is very effective at preventing mitochondrial damage when given early. Unfortunately, NAC therapy fails the majority of overdose patients because they seek medical attention too late. Interestingly, our preliminary data indicate that delayed interventions that scavenge ROS may actually delay regeneration and recovery. Thus, there is a critical need for a delayed targeted therapy that will benefit late presenting APAP overdose patients. Disruption of mitochondrial dynamics is a common feature of mitochondrial oxidant stress and the role of Mitochondrial Biogenesis (MB) in accelerating recovery and regeneration after injury has been reported in various organs. Also, mitochondria ROS/RNS has been shown to maintain cellular homeostasis by inducing MB as a compensatory mechanism. However, the role of MB in influencing regeneration after APAP overdose has not yet been studied. Thus, the goal of this proposal is to determine whether induction of MB would be a better strategy for promoting hepatocytes regeneration and liver recovery after APAP-mediated liver injury. Based on our preliminary data we developed the hypothesis, that APAP-induced mitochondrial oxidant stress has dual roles with higher levels, during the early injury phase, inducing hepatocyte necrosis and lower levels, at later times, activating the adaptive MB response. Therefore, further investigation of the benefit of MB induction as well as the effect of NAC on MB is necessary and will be the focus of this proposal. To achieve this goal, 3 aims will be investigated. The first aim will examine MB effect on liver regeneration after APAP overdose. The second aim will study the function of ROS/RNS production in relation with MB induction. The third aim will explore the role of MB and its outcome on recovery after APAP hepatotoxicity in models of human relevance such as HepaRG cells. This proposal has major health and clinical implications. It will clearly help clarify the role of MB in the liver in influencing clinical outcome after APAP overdose. It will also provide a clear answer to the effect of NAC on MB. If late NAC treatment negatively affects MB and liver regeneration, then a better therapy targeted at later stages of liver injury may need to be developed.